1. Field of the Invention
The present invention relates to an illumination device for exciting a fluorescent substance by irradiating the fluorescent substance with laser light from a laser irradiation device to emit visible light for use as illumination light.
2. Description of Related Art
Conventionally, there has been proposed a safety measure regarding a communication device that uses laser light to transmit and receive signals for avoiding the risk to the eye caused by light having high coherence emitted to the outside of the transmitter.
Taking as an example an infrared communication module described in Japanese Patent Application Laid-open No. 2003-258353, in a light source device used for a transmission device of the infrared communication module, liquid or swollen gel including a dynamic light scattering system (region including light scattering system) is placed in an optical path of light emitted from a semiconductor laser element, to thereby convert the light having high coherence to incoherent light, which is not harmful to the human, by dynamic multiple light scattering (Brownian motion) at the time when the light emitted from the semiconductor laser element passes through the region including the dynamic light scattering system.
As another example, Japanese Patent Application Laid-open No. 2006-352105 describes an optical transmission device, in which a light scattering member including light scattering particles for scattering laser light is placed in an optical path of light emitted from a semiconductor laser element, so that the light emitted from the semiconductor laser element is scattered while passing through the light scattering member to thereby convert the light having high coherence to incoherent light, which is not harmful to the human.
Further, there has also been proposed an illumination device for exciting a fluorescent substance by irradiating the fluorescent substance with laser light from a laser irradiation device to emit visible light, and for converting by a reflecting mirror the visible light into parallel rays for use as illumination light (see Japanese Patent Application Laid-open No. 2003-295319). Also in such illumination device, light having high coherence may leak to the outside to lead to the alleged risk of harming the eye. Japanese Patent Application Laid-open No. 2003-295319 describes, as a countermeasure against the case where the fluorescent substance cannot entirely absorb the laser light and transmits a portion of the laser light, a configuration in which a subreflecting mirror is placed in front of the fluorescent substance so that the laser light transmitted through the fluorescent substance is reflected by the subreflecting mirror to reenter the fluorescent substance and hence be entirely absorbed by the fluorescent substance.
In the illumination device for exciting the fluorescent substance by irradiating the fluorescent substance by the laser light from the laser irradiation device to emit the visible light for use as the illumination light, in the event that the laser light having high coherence for use as the excitation light for the fluorescent substance leaks, the risk to the human eye is assumed to be high. The possible reasons are: (1) optical elements of the laser irradiation device become out of alignment due to change/deformation of parts over time, external pressure or impact, or the like; (2) the fluorescent substance is displaced due to change/deformation of parts over time, external pressure or impact, or the like; and (3) the laser light is not entirely absorbed by the fluorescent substance and a portion of the laser light is transmitted through the fluorescent substance.
Japanese Patent Application Laid-open Nos. 2003-258353 and 2006-352105 each relate to a communication device. Therefore, it is suffice to place the region including the dynamic light scattering system or the light scattering member in contact with, or to be integrated with, the semiconductor laser element as the light source. However, in the illumination device, the fluorescent substance is irradiated with the laser light emitted from the semiconductor laser element to excite the fluorescent substance, and hence the positional relationship with the fluorescent substance should be considered. In this regard, Japanese Patent Application Laid-open Nos. 2003-258353 and 2006-352105 do not provide such knowledge.
Further, although Japanese Patent Application Laid-open No. 2003-295319 describes, in order to address the above-mentioned reason (3), the configuration using the subreflecting mirror in which the laser light transmitted through the fluorescent substance is reflected by the subreflecting mirror to reenter the fluorescent substance, the cases of the above-mentioned reasons (1) and (2) are not considered.